406 RAPID POPULATION GROWTH-1I
variable, if the findings of another investigator who could control for that variable show similar results.
The consistent trend of the consequences associated with either increasing family size or decreasing birth interval is striking and uniformly negative. When the full spectrum of these effects is seen, it is, in fact, alarming. No general survey or summary of the evidence concerning these effects could be found in the literature, although one portion of the spectrum, the effects on the survival of fetus and child, was reviewed recently by Day (6).
My intention here is to cover the full spectrum. Where possible, minimum essential information about the methodology of the study is given and relevant examples of the findings obtained are reviewed. The attempt is comprehensive but by no means exhaustive; it is impossible to review all available studies or all the findings of a given study. The chief criterion for inclusion here has been the clarity of the relationships shown by the data. No studies showing significant benefits associated with large families were excluded; none was found, although there were a few studies which showed no effects, either positive or negative.
THE EVIDENCE CONCERNING HEALTH CONSEQUENCES OF FAMILY SIZE
Studies which have examined the effects associated with family size, number of children, number of siblings, or parity of the mother (the number of children born to a mother) are far more numerous than those considering birth or pregnancy interval. Because of the thoroughness and variety of the evidence concerning family size, it will be considered first.
Tlie Effects on Children
Much of the data that are available concern the effects on children and are derived from studies of mortality and morbidity of various types, including malnutrition and anomalies in growth and intelligence.
Family Size and Morbidity. Several factors commonly associated with increased incidence of illness are also associated with increased family si/e. Among these, economic limitations, crowding, and generally poor sanitary conditions stand out. The stage is set for causal interaction.
The longitudinal study of families of all social classes in Cleveland, Ohio, carried out by Dingle and his associates (7) showed as clearly as any the association between family size and illness. They examined the incidence of various common illnesses by family size. As an example, their findings with
monnft tn infprtinnc crnQtrnpntpritis tire shown in Tnblp, 1 . Not rmlv Hnr>« Ihn